16a.c

   1 #include <stdio.h>
   2 #include <stdlib.h>
   3 #include <string.h>
   4 #include <stdint.h>
   5
   6 char *hex2bin[] = { ['0'] = "0000" , ['1'] = "0001" , ['2'] = "0010" , ['3'] = "0011" , ['4'] = "0100" , ['5'] = "0101" , ['6'] = "0110" , ['7'] = "0111" , ['8'] = "1000" , ['9'] = "1001" , ['A'] = "1010" , ['B'] = "1011" , ['C'] = "1100" , ['D'] = "1101" , ['E'] = "1110" , ['F'] = "1111", ['\n'] = "0000"};
   7
   8 struct stream {
   9         int pos;
  10         char *buf;
  11 };
  12
  13 int next(struct stream *f)
  14 {
  15         if (*f->buf == '\0') {
  16                 int c = getchar();
  17                 if (c == EOF) {
  18                         printf("EOF\n");
  19                         exit(1);
  20                 }
  21                 f->buf = hex2bin[c];
  22         }
  23         int r =*f->buf == '1' ? 1 : 0;
  24         f->buf++;
  25         f->pos++;
  26         return r;
  27 }
  28
  29 int bin2int(struct stream *f, int n)
  30 {
  31         int r = 0;
  32         for (int i = 0; i<n; i++)
  33                 r = 2*r+next(f);
  34         return r;
  35 }
  36
  37 int parse_packet(struct stream *f)
  38 {
  39         int packetversion = bin2int(f, 3);
  40         int packettype = bin2int(f, 3);
  41
  42         switch (packettype) {
  43         //Literal value
  44         case 4: {
  45                 int num = 0;
  46                 while (next(f) == 1) {
  47                         num = num*16+bin2int(f, 4);
  48                 }
  49                 num = num*16+bin2int(f, 4);
  50                 break;
  51         }
  52         default: {
  53                 int lengthtypeid = next(f);
  54
  55                 //length is 15
  56                 if (lengthtypeid == 0) {
  57                         int lengthsubpackets = bin2int(f, 15);
  58                         int oldpos = f->pos;
  59
  60                         while (f->pos - oldpos < lengthsubpackets)
  61                                 packetversion += parse_packet(f);
  62                 } else {
  63                         int numsubpackets = bin2int(f, 11);
  64                         for (int i = 0; i<numsubpackets; i++)
  65                                 packetversion += parse_packet(f);
  66                 }
  67                 break;
  68         }}
  69         return packetversion;
  70 }
  71
  72 int main()
  73 {
  74         struct stream f = {.pos=0, .buf=""};
  75
  76         int r = parse_packet(&f);
  77         printf("r: %d\n", r);
  78 }